Magellanic Horned Owl's Retreat: Nest and Prey Remains

By Bruce G. Marcot, Ecology Picture of the Week:

In March of 2004, I found myself climbing the side of a large rock outcrop northeast of the town of Bariloche, southern Argentina.  I was in the steppe country of southern Patagonia, in Perito Moreno along a lagoon called Los Juncos.  On the side of the rock outcrop was sign -- drippy fecal "whitewash" -- of an active nest of Magellanic (or Magellan) Horned Owls.

Magellanic Horned Owls are large owls of the genus Bubo -- the same genus as the widespread Great Horned Owl of North, Central, and South America, from which the species was recently split.  Magellanic Horned Owls occur in southern South America, are mostly crepuscular and nocturnal, and their behavior is little studied.

As it turned out, no one was home in the nest at that time, so I collected feathers and owl pellets from the nest site and along the ground below the nest ledge, and also from a second nest on another nearby outcrop called "Elephant Rock" (which is shaped rather like an elephant from one perspective).  

Interestingly, on Elephant Rock I also discovered two other active nests, on high ledges, built of heavy sticks by Black-chested Buzzard-eagles.  Apparently, these eagles and Magellanic Horned Owls can occupy the same cliff site at the same time!

Owl pellets (or castings) are the regurgitated remains of the animals that the owl eats.  I later dissected the pellets to determine what kinds of small mammals these Magellanic Horned Owls were preying upon. The prey remains -- typical in an owl pellet -- included skulls, jaw bones, whole legs and leg bones, hairs, and fractured bits of other bones.

So what do these Magellanic Horned Owls consume?  Click on the individual jaw bone prey items in the following figure to find out, and keep reading below!

Overall, these prey items I identified are typical of the species in this area of Argentina.  Additional prey remains I found included European hares (an introduced species there) and tuco-tucos (gopher-like digging rodents).  

  --Bruce G. Marcot

Image and text © Bruce G. Marcot, Ph.D. Research Wildlife Ecologist,
who produces the Ecology Picture of the Week website.